U.S. Pat. No. 3,859,527 describes a method for recording and reproducing a high-energy radiation image using a panel for storing a radiation image comprising a stimulable phosphor which emits light when stimulated with visible or infrared radiations after exposure to such radiation (wherein high-energy radiation means an electromagnetic wave or corpuscular radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, neutrons, ultraviolet rays, or the like).
U.S. Pat. No. 4,258,264 describes a method and apparatus for reproducing a radiation image by stimulating a storing phosphor with stimulating rays, the wavelengths of which are in the range from 600 to 700 nm, and detecting the stimulated light by means of a light detector, the detected light being in the range from 300 to 500 nm.
EP 159,726 describes an alkali earth metal halide phosphor activated with divalent europium having the formula: EQU M"X.sub.2.aM"X'.sub.2.bA:xEu.sup.2+
wherein M" is at least one alkali earth metal selected within the group consisting of Ba, Sr and Ca; both X and X' are at least a halogen selected within the group consisting of Cl, Br and I, X being different from X'; A is at least one oxide selected within the group consisting of SiO.sub.2 and P.sub.2 O.sub.5 ; a, b and x are numbers respectively satisfying the conditions 0.1.ltoreq.a.ltoreq.10; 10.sup.-4 .ltoreq.b.ltoreq.0.2 and 0&lt;x.ltoreq.0.2. In the above mentioned patent application there are also described a method for recording and reproducing a radiation image using said phosphor and a radiation image storing panel using such phosphor. The radiations stimulating said phosphor preferably have a wavelength in the range from 500 to 800 nm.
EP 107,192 describes a method for recording and reproducing a radiation image comprising the steps of (i) causing a stimulable phosphor to absorb radiation after passing through an object, (ii) exposing said stimulable phosphor to an electromagnetic wave having a wavelength in the range from 450 to 800 nm to release the stored radiation energy as fluorescent light and (iii) detecting said fluorescent light, wherein said stimulable phosphor is a divalent europium activated complex halide having the formula: EQU M"FX.aM'X'.bM'"X".sub.2.cM'"X'".sub.3.xA:yEu.sup.2+
wherein M" is at least an alkali earth metal selected within the group consisting of Ba, Sr and Ca; M' is am alkali metal selected within the group consisting of Li, Na, K, Rb and Cs; M'" is at least a trivalent metal selected within the group consisting of Al, Ga, In and TI; A is at least a metal oxide; X is at least a halogen selected within the group consisting of Cl, Br and I; each of X', X" and X'" are at least a halogen selected within the group consisting of Cl, Br and I; a, b and c are numbers respectively satisfying the conditions 0.ltoreq.a.ltoreq.2; 0.ltoreq.b.ltoreq.0.01; 0.ltoreq.c.ltoreq.0.01 and a+b+c.ltoreq.10.sup.-6 ; x and y are numbers respectively satisfying the conditions 0&lt;x.ltoreq.0.5 and 0&lt;y.ltoreq.0.2. Such patent application describes also a radiation image storing panel used for such a method.
The phosphors described in the above cited EP 159,726 and 107,192 give the best results, with respect to the emission efficiency, when they are stimulated with radiation having a wavelength in the range from 600 to 700 nm, in particular when they are stimulated with a He-Ne 633 nm laser beam. Such phosphors do not give such good results when they are stimulated with radiation having a wavelength lower than 600 nm.
EP 111,893 describes a method for recording and reproducing a radiation image comprising the steps of (i) causing a radiation image storing panel to absorb a radiation after passing through an object, such a panel containing a divalent europium activated barium fluorochloride phosphor, (ii) exposing said panel to an electromagnetic wave having a wavelength in the range from 400 to 550 nm to release the stored radiation energy as fluorescent light and (iii) detecting said fluorescent light.
EP 174,875 describes a method for converting radiographic images comprising the steps of (i) storing a radiation energy corresponding to a radiographic image in a stimulable phosphor panel, (ii) scanning the panel with a stimulating ray to release the stored energy as a fluorescence, and (iii) detecting the fluorescence to form an image, wherein the stimulable phosphor is represented by the following formula: EQU (M.sub.1-x M'.sub.x)X.aM"X'.sub.2.bM'"X".sub.3.cA:dB
wherein M is Cs or Rb; M' is Li, Na, K, Rb or Cs; M" is Be, Mg, Ca, Sr, Ba, Zn, Cd, Cu and Ni; M"' is Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Al, Ga and In; A is BaO, MgO, CaO, SrO, BeO, ZnO, Al.sub.2 O.sub.3, Y.sub.2 O.sub.3, La.sub.2 O.sub.3, In.sub.2 O.sub.3, SiO.sub.2, TiO.sub.2, GeO.sub.2, SnO.sub.2, Nb.sub.2 O.sub.2, Ta.sub.2 O.sub.5 and ThO.sub.2 ; B is Eu, Tb, Ce, Tm, Dy, Pr, Ho, Nd, Yb, Er, Gd, Lu, Sm, Y, TI, Na, Ag, Cu, Mg, Pb, Bi, Mn and In; X, X' and X" are F, Cl, Br and I.
EP 304,121 describes a method for recording and reproducing an X-ray image which comprises the steps of: (i) causing a photostimulable phosphor to absorb image-wise modulated X-rays, (ii) photostimulating said phosphor with stimulating electromagnetic radiation selected from visible light and infrared light to release from the phosphor in accordance with the absorbed X-ray electromagnetic radiation different in wavelength characteristic from the radiation used in the photostimulation, and (iii) detecting said light emitted by photostimulation, wherein said phosphor is an europium or cerium activated halo-silicate of formula: EQU M.sub.x M'.sub.z Si.sub.y O.sub.x+2y X.sub.2z :aA',bA"
wherein M and M' are selected from the group consisting of Ca, Sr. Ba, Mg, Cd, Zn, and Pb, X is selected from the group consisting of Cl, Br, and I A' is selected from the group consisting of Eu.sup.2+ and Ce.sup.3+ and A" is selected from the group consisting of La, Y, Sc, and the lanthanide elements. The values of x, y and z are in the range of from 0.5 to 3.5, 0.5 to 3.5 and 0.1 to 4.5, respectively.
EP 391,153 describes phosphors to be used in a method for reproducing a radiation image by stimulating a storing phosphor with stimulating rays and detecting the stimulated light by means of a light detector wherein said phosphors are rare earth orthosilicates activated with Ce and/or Tb and co-activated with Zr and/or Sm.
JP patent application 49/97785 discloses an yttrium and gadolinium halo-silicate phosphor for flying spot tubes having the following formula: EQU Ln.sub.1-x-y Ce.sub.x Tb.sub.y Si.sub.u O.sub.v Cl.sub.w
wherein Ln is Y and/or Gd. 0.001.ltoreq.x.ltoreq.0.15, 0.ltoreq.y.ltoreq.0.09, 0.65.ltoreq.u.ltoreq.0.7, 0.2w.ltoreq.0.6 and 3+4u=2v+w.
In the Journal of the Electrochemical Society, March 1978, Vol. 125, No. 3, pp. 445-448, W. Lehmann and Th. J. Isaacs describe the luminescent properties of lanthanum and yttrium halo-silicates of the approximate composition LnSiO.sub.3 X, wherein Ln is La or Y, and X is F, Cl, and Br, activated with several activators, such as, Ce, Tb, Sm, Dy, Eu. The preparation and the structural properties of these phosphors are also described.
H. Yamada, T. Kano and M. Tanabe in Materials Research Bulletin, Volume 13, No. 2, pp 101-108 (1978) disclose the luminescent properties of yttrium and gadolinium halo-silicates having composition Y.sub.3 Si.sub.2 O.sub.8 Cl and Gd.sub.3 Si.sub.2 O.sub.8 Cl, activated with cerium. A method of preparation and the structural properties are also disclosed.
None of the above patent and literature references relating to stimulable phosphors suggests the use of rare-earth halo-silicate phosphors as photostimulable phosphors in a method similar to that described in the U.S. Pat. Nos. 3,859,527 and 4,239,968.